As disclosed in JP-A-2002-336579, conventional household sewing machines have been used in which a needle plate is constructed by a first needle plate fixed to a sewing machine bed and a second needle plate (referred to as a first lid in the above disclosure) detachably attached to the sewing machine bed. The first needle plate is formed in an oblong shape and is made of a metal plate (steel plate) having a needle hole for penetration of sewing needle therethrough and a square hole for projecting and retracting a feed dog for feeding a workpiece cloth. The second needle plate is formed in an L-shape and is located along the left and front side of the first needle plate. The first needle plate is made of metal so as to tolerate the striking of the sewing needle thereon. The second needle plate, on the other hand, merely supports a cloth on the upper surface thereof and is not struck by the sewing needle. Hence, the second needle plate is made of synthetic resin for cost reduction.
The following construction is adopted to render the detachable attachment of the second needle plate. Four pieces of L-shaped (in side view) hooks are integrally provided on the underside of the second needle plate; more specifically, on the left and right portions respectively of the longitudinal ends of the underside. On the other hand, four recesses are provided for accommodating the aforementioned hooks; three on the sewing machine bed and one on the underside of the first needle plate. Also, a positioning notch for lateral positioning is formed on the right rear-end portion of the second needle plate, and a protrusion for engagement with the notch is provided on the right front-end portion of the first needle plate. Also a small (few mm) space is defined between the front end of the second needle plate and an opening of the sewing machine bed.
Thus, upon attachment of the second needle plate, the second needle plate is fitted from above to an opening portion defined on the sewing machine bed 1 and slightly (few mm) pushed toward the rear. Thus the elasticity of the four hooks engages themselves with each recess. Also, upon removing the second needle plate, the second needle plate is slightly (few mm) pulled toward the front so as to be disengaged, and thereafter lifted upward.
In such sewing machine, by removing the second needle plate from the sewing machine bed, the upper surface of the sewing machine bed reveals an L-shaped opening and exposes therein a horizontal hook mechanism. Thus, cleaning and trouble shooting work such as removing the bobbin thread tangled to the horizontal hook can be carried out. As compared to the case in which the entire needle plate is removed, the open space created on the sewing machine bed is minimized, thereby preventing the intrusion of dust and foreign objects to the possible extent. Also, the needle hole and the square hole are no longer displaced upon removing the needle plate.
However, under the above described needle plate construction, since the second needle plate made of synthetic resin is engaged with the needle plate and the sewing machine bed by the elasticity of the second needle plate itself, the operational burden incurred by the second needle plate upon attachment/detachment thereof causes the transformation of the hooks. Also, the location of the second needle plate attached to the sewing machine bed with respect to the location of the first needle plate fixed to the sewing machine frame is prone to vary, therefore causing some degree of rattle in the mating surfaces of the first and the second needle plates.
One of the solutions to the above problem is manufacturing the second needle plate also from metal and detachably attaching the second needle plate to the first needle plate with a fastening screw. However, this requires tightening and loosening of the screw upon attachment/detachment of the second needle plate, consequently requiring tools therefor, and complicating the attachment/detachment work.